function getData(endpoint, cb) {
  return new Promise((resolve,reject) =>{
    const xhr = new XMLHttpRequest();

    xhr.open('GET', endpoint);

    xhr.onreadystatechange = function () {
      if (this.readyState === 4) {
        if (this.status ===200) {
          resolve(JSON.parse(this.responseText));
    }  else {
        reject('Something went wrong');
  }
}
  };

  setTimeout(() => {
    xhr.send();
  }, Math.floor(Math.random() * 3000) + 1000);
});
}

getData('./movies1.json')
.then(movies => {
console.log(movies);
return getData('./actors.json');
})
.then(actors => {
console.log(actors);
return getData('./directors.json');
})
.then(directors => {
console.log(directors);
})
.catch(error => {
console.log("出现了问题");
});
